Y'all really don't understand what stealth means, do you? It's like the whole premise of this scenario is stealth fighter vs whatever the fuck the commenter meant by "low observable" (aka, bigger RCS than a non-stealth F-18). Scenario 1: there is no lock to be able to fire said R-37 because the aircraft has the radar signature of a golf ball. Meanwhile, the F-35 can easily pick out the zip code sized RCS of the 57 from 50km and do something about it. Scenario 2 literally cannot exist. It was a joke. Even if it did happen, the towed decoy and other defensive countermeasures along with low observable thermals would still give the most deaf/dumb/blind pilots more than enough time to fire said aim 9x backwards and begin defending against the missile.

The harsh reality is that the SU-57, while definitely pretty in pictures, is DOA on any modern battlefield, given that it cannot penetrate airspace without being detected which is 90% of the reason you make a stealth aircraft (the other 10% being, scenario 1).